Method for preparing dimensionally stable plastic surface coverings

ABSTRACT

A flexible, dimensionally stable plastic surface covering having a non-foamed poly(vinyl chloride) layer containing cross-linked polymer positioned between two foamed poly(vinyl chloride) layers, and having a wear resistant top coat on the surface of the system. One or more of the foamed surfaces may be embossed, and the top foamed surface may carry a printed decoration thereon.

United States Patent 1191 Witman [4 1 June 25, 1974 METHOD FOR PREPARING3,213,071 10/1965 Campbell 156/79 x IM SIO STABLE PLASTIC CWitmlan i:

, row e 7 SURFACE COVERINGS 3,538,204 11/1970 Grubb.. 264/46 X [75]Inventor: Jack H. Witman, Lancaster, Pa, 3,591,401 7/1971 Snyder et a1264/47 X 3,608,006 9/1971 HOSOdfl et a1 156/79 [731 Asslgneei -F 8 CorkCompany 3,645,837 2/1972 Chisholm 8181 264/47 x Lancaster, 3,657,0364/1972 Millenhoff et al. 156/79 X [22] Filed June 1972 PrimaryExaminer-George F. Lesmes I 1 PP .1 266,585 Assistant Examiner-StanleyS. Silverman Attorney, Agent, or FirmTheodore L. Thomas [52] US. Cl156/79, 117/72, Il7/138.8 A,

117/116,161/124,161/160,161/161, 1571 ABSTRACT 161/166, l61/DIG. 3,264/47, 264/52 A flexible, dimensionally stable plastic surface cover-[511 Int. Cl B32b 5/18, B32b 31/14 ing having a non-foamed poly(vinylchloride) layer [58] Field of Search 156/79; 264/47, 52; containingcross-linked polymer positioned between 161/160, 161, 116, 124, DIG. 3;117/l38.8 two foamed po1y(vinyl chloride) layers, and having a A, 138.8E, 72 wear resistant top coat on the surface of the system.

One or more of the foamed surfaces may be em- [56] References Citedbossed, and the top foamed surface may carry a UNITED STATES PATENTSprinted decoration thereon.

2,941,917 6/1960 Anspon et a1 161/254 7 Claims, 3 Drawing Figures VINYLRESIN BLENDING PLASTICIZER BLOWING AGENT FORMING GELLED SHEET APPLYINGNONFOAMABLE PLASTISOL CONTAINING POLYMERIZABLE MONOMER AND CATALYSTGELLING NONFOAMABLE LAYER BACKING OPTIONAL APPLYING FOAMABLE VINYLPLASTISOL agkgfig GELLING FOAMABLE LAYER APPLYING CLEAR VINYL WEAR COATAND HEAT TO FUSE RESIN, DECOMPOSE BLOWING AGENT POLYMERIZE MONOMERPRODUCT OPTIONAL PRINTING WITH CATALYST-CONTAINING INK Pmimnwuz w5.819.438

fi 1 fi7- 'SLIGHTLY FOAMED LEAR REsIN LAYER CLEAR RESIN AYER ES FOAMEDRESIN LAYER L REGIONS POLYMERIZED n a I 4 v u 's er E a TNHN'NG "1011311,, LAYER a a RQQ'I N BACK'NG BACKING gggm POLYMERIZED REsIN LAYERLAYER STRENGTHENING LAYER VINYL RESlN BLENDING -PLAsTIcIzER I BLOWINGAGENT FORMING i GELLED sI-IEET BACK'NG APPLYING NONFOAMABLE PLAsTIsoLcoNTAINING POLYMERIZABLE MONOMER AND cATALYsT GELLING NONFOAMABLE LAYEROPTIONAL APPLYING FOAMABLE -POLYMERIZABLE VINYL PTASTISOL MONOMERGELLING FOAMABLE LAYER I oPTIoNAL PRINTING WITH CATALYST-CONTAINING INKAPPLYING CLEAR VINYL WEAR COAT HEAT TO FUSE RESIN DECOMPOSE BLOWINGAGENT AND POLYMERIZE MONOMER PRODUCT BACKGROUND OF THE INVENTION 1.Field of the Invention This invention relates to flexible, foamedplastic surface covering having a strengthening or dimensionallystabilizing layer containing cross-linked polymer between two foamlayers. This invention also relates to such a structure wherein afluid-supplied intermediate coating including a polymerizable monomerand a catalyst therefor is polymerized in situ to form such astrengthening layer. The invention in one important embodiment is animprovement over the foamed surface covering described and claimed inU.S. Pat. No. 3,3 65,35 3-Witman, the disclosure of which isincorporated herein by reference.

2. Description of the Prior Art In the manufacture of surface coveringsin general and flexible floor coverings in particular, it has beenpreviously known to include an intermediate layer such as a scrimmaterial in a laminated structure of this type to strengthen anddimensionally stabilize the structure. These prior methods, however,involved width and processing problems which rendered wide coveringseconomically unattractive.

The prior art also includes the use of various adhesives to secure thelaminae of plastic floor coverings together, but adhesives may allowseparation of laminae during processing and changes in dimension of theproduct.

U.S. Pat. No. 3,196,030-Petry teaches the formation of a reinforcinglayer in a vinyl foam surface covering by passing a vinyl foam sheetbetween densifying rolls while a layer of the vinyl foam is hot enoughto be permanently collapsed to form the reinforcing layer.

U.S. Pat. No. 2,941,917 discloses a method of making laminated polymersheets of rigid, transparent material having a strengthening inner layerby polymerizing, by use of a catalyst and/r application of heat, anacrylic or methacrylic ester monomer layer between two external layersof polymethyl a-chloroacrylate.

U.S. Pat. No. 3,558,427 teaches adding a polymerizable monomer and apolymerization catalyst to a slurry of fibers and binder in a beatersaturation process, forming a sheet therefrom, and subjecting the sheetto heat to bring about polymerization of the monomer.

The prior art methods do not teach the provision in a flexible, foamedplastic floor covering of an intermediate, fluid-applied, strengtheninglayer which is flexible, resists stretch, and which stabilizes the floorcovering during use. In addition, width limitations normally encounteredin the use of glass scrim material and the like as the intermediatestrengthening layer in a structure of this type are eliminated.

SUMMARY OF THE INVENTION The method of the invention contemplatesforming a dimensionally stable plastic surface covering by forming andgelling a foamable poly( vinyl) chloride) layer on a backing, applyingas a fluid and gelling a nonfoamable coating at least 4 mils thick ofpoly(vinyl non-foamable layer, applying a clear non-foamable poly(vinylchloride) top coating, and heating the entire system to a temperaturesufficiently high to fuse and foam the resins and cause thepolymerization catalyst to polymerize and cross-link the monomer in theintermediate, non-foamable layer, thus forming a foamed, flexibleplastic surface having a tough, dimensionally stabilizing inner layer.The two foamed layers may have different densities, and preferably thetop foamed layer will have the higher density.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a cross-sectional view of thesmoothsurfaced product of this invention,

FIG. 2 is a cross-sectional view of an embossed product obtained byinclusion of certain optional steps in the process of this invention,and

FIG. 3 is a simplified flow diagram of the preferred process of thepresent invention. The legends on all figures are self-explanatory.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The thermoplastic resins usefulin forming the foamed and unfoamed lamina of the surface covering of thepresent invention are those resins capable of forming films and sheets.Poly(vinyl chloride) is the preferred resin, although copolymers ofvinyl chloride with minor proportions of other materials such as vinylacetate, vinylidene chloride, other vinyl esters such as vinylproprionate, vinyl butyrate, as well as alkyl substi tuted vinyl estersmay be used. The glass transition temperature of these resins is thetemperature at which the resin changes from a hard, brittle solid to aflexible solid. Increasing plasticization of the resin increasinglylowers the glass transition temperature.

In making the surface covering according to the method of thisinvention, the thermoplastic resin, preferably poly( vinyl chloride) asdescribed above, will be combined with a plasticizer therefor and otherdesired ingredients to form a plastisol in a known manner such as thosedescribed in aforesaid U.S. Pat. No. 3,365,353-Witman. The plastisol maythen be conveniently applied to a substrate and gelled to form a sheet.Suitable plasticizers are the ester-type plasticizers such as dioctylphthalate, dioctyl sebacate, dioctyl adipate, diocytl azelate, in whichthe octyl group is frequently in the form of a 2-ethyl hexyl group.Other alkyl groups can be used in place of the octyl group to yield, forexample, plasticizers such as dibutyl phthalate, dibutyl sebacate,dibutyl adipate, and the like. The phosphate esters are also useful, forexample tricresyl phosphate. The viscosity of the plastisol may becontrolled to some extent by selection of a particular plasticizer, theparticular resin, and the amounts of each to be used. Hence a range inviscosity is available depending on how a sheet is to be formed from theplastisol.

The blowing agent used in forming the foamed lamina of the surfacecovering of this invention must be thoroughly distributed throughout theresin-plasticizer mixture. A variety of blowing agents is available onthe market for incorporation in thermoplastic resins. The preferredblowing agent for poly(vinyl chloride) is azodicarbonamide whichnormally decomposes at a temperature of about 390 F. in air. Thisblowing agent is particularly suitable for use in the method of thepresent invention in view of its relatively high decompositiontemperature. The following table shows other usable blowing agents withthe temperature at which they release gas vigorously in dioctylphthalate:

The usable blowing agents will generally comprise the substitutedhydrazides, substituted azo compounds, are substituted nitrosocompounds. In the plastisol used for forming the low density foamed basesheet or lamina, the blowing agent will normally be present in an amountin the range of about 1.5 to 5 percent based on the weight of thethermoplastic resin. In the plastisol used for forming the higherdensity foamed top lamina, the blowing agent will normally be present inan amount in the range of about 1 to 4 percent based on the weight ofthe thermoplastic resin. As a general rule, the preferred minimumdecomposition temperature of the blowing agent should be about 320 F.and the blowing agent should decompose below the decompositiontemperature of the resin, which in the case of poly(vinyl chloride)would be about 400 F. However, stabilized vinyl resin composition willnormally not decompose until even higher temperaturesapproaching 450F.are reached.

To these critical ingredients, namely, the resin, the plasticizer, andthe blowing agent, additional ingredients such as blowing agentactivators, pigments, dyes, or other decorative elements may be added tothe composition to be formed into the sheets. Depending on the materialused and the intensity of the color desired, the amounts of such extraadditives will normally range from a small fraction of a percent to 20percent by weight of the total composition. Relatively small amounts ofa granular filler such as a clay, a limestone, or a silicate may beused. However, the foamable compositions will not be highly filled inview of a need for at least a portion thereof to expand and form acellular or foamed layer. Fillers to be used, if any, will normally bepresent in less than about 20 percent by weight of the totalcomposition. Blowing agent activators or accelerators such as the leadand zinc salts of organic acids will be present in amounts of 0.5 to 3parts by weight per hundred of resin. Small amounts of heat and lightstabilizers will also be incorporated. These are known in the art andmay comprise the bariumcadmium salts of long-chain fatty acids, polyolssuch as pentaerythritol or alpha-methylglucoside, nitrogen compoundssuch as melamine or dicyandiamide, esters such as phenyl phthalate,phenyl benzoate, o-toluol benzoate, triethylene glycol salicylates,certain of the organic phosphates, and mixtures thereof. Suchstabilizers will not normally be present in amounts greater than about 3percent by weight of the total corriposition.

In making the foamable lamina of the surface covering of this invention,the several ingredients will be blended to achieve thorough distributionof one in the other in customary manner well known in the art. Afterthorough mixing has been achieved, the plastisol is formed into a sheet.

In forming the base sheet of the surface covering of this invention, theplastisol may be doctored, roll coated, or otherwise applied to abacking or to a strippable carrier which may be a steel belt, a rubberbelt, paper, or a felt having a release coating thereon. Application ofrelatively gentle heat to the plastisol causes a low degree of fusionand thus gels and slightly sets the sheet so it may be removed orotherwise handled for further treatment. The amount of heat applied atthis stage of the process is insufficient to decompose the blowingagent. The plastisol may also be applied directly onto a backing whichis to become a permanent part of the surface covering. The backing wouldbe one suitable for use as a surface covering, for example, a felt,preferably a rubber-bonded asbestos backing, a vinyl sheet backing, acellulosic felt or other backing which lends itself to surface coveringapplications.

Instead of a plastisol, an organosol may be used in which an organicsolvent is added to the resinplasticizer mixture. The addition of suchsolvents is a further control in the viscosity of the fluid, and suchsolvents as the ketones, for example, methyl ethyl ketone and methylisobutyl ketone, may be used. I-Iydrocarbon aromatic solvents may beused, for example toluene and xylene. Aliphatics may be used such as areobtained in certain cuts from fractionation of hydrocarbon mixtures usedin the oil industry. A disadvantage, however, of using an organosolinstead of a straight plastisol in the present process is that thesolvent will be driven off during the incipient gelation stage and musteither be recovered or otherwise removed from the sphere of operationswhen heat is applied to the organosol.

The top, or high density foamed lamina of the surface covering of thisinvention is produced using essentially the same process and ingredientsas that used to form the foamable base sheet with the exception that alesser amount of blowing agent is used in the top sheet, therebyresulting in a higher density sheet. Suitable selection and/or variationin the type and amount of blowing agent accelerator may also be utilizedto vary the density of the sheet.

The process so far has produced thermoplastic sheets which will normallyhave at this stage of the process a thickness of the bottom sheet in therange of about 0.005 to 0.050 inch, exclusive of any backing, and a topsheet thickness in the range of about 0.004 to 0.040 inch. The sheetswill contain thoroughly distributed therein a blowing agent in conditionto liberate gas when sufficient heat has been applied thereto.

The non-foamable strengthening layer to be formed between the foamablebase sheet and the foamable top sheet is formed utilizing the resins andplasticizers previously described in connection with the foamablelamina. In forming this strengthening layer, the blowing agent isomitted and a polymerizable monomer and a polymerization catalysttherefor are included. The monomer used must have at least twoolefinically unsaturated sites in its molecule. Not only does themonomer polymerize and crosslink under the conditions to be describedbelow, but it, or the polymerization catalyst, will also apparentlycause cross-linking of the poly(vinyl chloride) chains. Thecross-linking imparts particular strength to the reinforcing layer andcauses significant improvement in the dimensional stability of thefinished product. The monomer must be compatible with the vinyl resin,that is, it must be miscible therewith and be capable of beingintimately dispersed therein instead of occupying discrete volumes inthe plastisol. Examples of usable polymerizable monomers are the diandpolyacrylates and methacrylates prepared by the esterification ofalcohols with acrylic acid and methacrylic acid. Monoacrylates andmethacrylates are usable where the esterifying portion of the alcoholitself contains an olefinically unsaturated bond, as is the case inallyl acrylates. Dicarboxylic acids may be esterified with unsaturatedalcohol to produce such usable monomers as diallyl fumarate.Diolefinically unsaturated hydrocarbons such as divinyl benzenes,divinyl toluene, and the like also function to polymerize and tocross-link in the present process. As used herein, the term monomermeans a compound of relatively low molecular weight compared with thepolymers it forms. As emphasized above, the only requirement for thispolymerizable monomer is that it be compatible with the plastisol systemand that it have two olefinically unsaturated sites in the moleculewhich will allow the compound to polymerize and cross-link under theconditions of temperature and catalyst to be described below. Thepolymerizable monomer, depending on the composition, will generally bepresent in the range of about 5 to 75 percent by weight based on theweight of the thermoplastic resin.

The catalysts used in forming the non-foamable, polymerizable layer ofthe surface covering of this invention are the known free radicalcatalysts widely used to enhance polymerization of olefinicallyunsaturated compounds. They comprise primarily the organicper-compounds. Among the peroxides that are usable are di-t-butylperoxide, benzoyl peroxide, lauroyl peroxide, capryloyl peroxide, acetylperoxide, pchlorobenzoyl peroxide, cumene hydroperoxide, cycloh'exanoneperoxide, t-butyl peracetate, and the other known peroxide initiators.Large numbers of such peroxides exist, and generally they are brokendown into broader groups comprising low-temperature types,intermediate-temperature types, and high-temperature types. Thehigh-temperature types are those generally decomposing above 250F. Otherper-compounds such as t-butyl perbenzoate, and isopropyl-percarbonateare usable in the present process. Besides the percompound type offree-radical initiators, there may be used such aliphatic azocatalystsas alpha,alpha'- azodiisobutyronitrile.

In forming the non-foamable strengthening layer, the resin, plasticizer,monomer, and catalyst are mixed. The catalyst may require a carrierliquid which is preferably a diluent, solvent, or plasticizer for theparticular resin in the plastic sheet. For example, a mixture of methylethyl ketone and dioxane serves as an excellent carrier for many ofthese catalysts. The liquid chosen should be such that the catalyst issoluble therein, or at least partly soluble therein, in order thatmaximum contact be established between the catalyst and thepolymerizable monomer distributed throughout the plastisol. Where thecatalyst is soluble in plasticizers such as tributoxy ethyl phosphiteand dibutyl phthalate, then the plasticizers alone may serve as carriersfor the catalyst.

Application of the plastisol containing the catalyst and monomer may becarried out in any convenient manner, such as by doctoring, rollcoating, printing,

curtain coating, or any other convenient manner in a thickness of atleast 4 mils to provide the required strength. Depending on the use ofthe final product, the strengthening layer may be as much as mils inthickness.

In making the surface covering of this invention as previously stated,the bottom foamable plastisol layer may be applied to a permanentbacking or to a strippable carrier followed by the application ofrelatively gentle heat to gel the sheet. To the sheet so formed is thenapplied and gelled the liquid plastisol containing the polymerizablemonomer and the catalyst therefor. Onto this is then applied the topfoamable plastisol layer which was made as previously described. A clearplastisol wear layer may be then applied over the top foamable layer andthe composite structure may then be heated to a temperature in the rangesufficiently high that the polymerization catalyst initiatespolymerization of the polymerizable monomer in the intermediatestrengthening layer and foams and fuses the resin in the remaininglayers.

An embossed appearance may be achieved on the surface covering of thisinvention by including in the composition of the top foamable layer apolymerizable monomer of the same characteristics as those described foruse in the non-foamable reinforcing layer. The top layer would beprinted with a decorative pattern, and one or more of the inks wouldcontain a poly merization catalyst, the process being set forth in theaforesaid US. Pat. No. 3,365,353-Witman. Mechanical embossing can beused.

The following examples illustrate several embodiments of the invention.All parts are by weight unless otherwise stated.

Example 1 The following plastisol was prepared by thoroughly mixing thefollowing ingredients in a change-can mixer.

Another plastisol was formed in a similar manner by mixing the followingingredients in a change-can mixer.

Ingredients Parts Poly(vinyl chloride) resins 3000.0 Di-Z-ethyl hexylphthalate 1 167.0 Epoxidized tallate 150.0 Zinc octoate 60.0TlO2/DOPZ58/4Z 252.0 Azodicarbonamide/DOP:60/40 150.0

Non-foamable plastisol was formed by thoroughly mixing the followingingredients.

Ingredients Parts Poly(vinyl chloride) resins 3000.0 Di-2-ethyl hexylphthalate 2l0.0 Epoxidized tallate 150.0 Calcium carbonate 300.0Trimethylol propane trimethacrylate 900.0 Pigment dispersion 30.0Lauroyl peroxide 2.7

The first-formed plastisol was applied on a releasable backing having athickness of 0.042 inch. The plastisol was applied with a reverse rollcoater in a wet thickness of 22 mils. The plastisol-coated backing wasgelled in an oven for 1 /2 minutes at 385F.

The nonfoamable fluid plastisol was then applied by means of a reverseroll coater in a wet thickness of mils onto the first-formed sheet andgelled at 275F. for 3 minutes. The second foamable plastisol coating ortop foamable coating was then applied and gelled in an oven for 4minutes at 275F. A clear coating of poly(vinyl chloride) plastisol wasthen applied over the entire sheet. The composite structure was thenheated at about 385F. for 3% minutes to cause fusion of the resin,decomposition of the blowing agent, and polymerization of the monomer.The clear coat also fused and became an integral part of the systemcovering the sheet. A strong, flexible, dimensionally stable sheetresulted.

Example 2 Restrictor lnk Formula Parts Poly(vinyl chloride)/poly(vinylacetate) 25.0

copolymer Benzoyl peroxide/dibutyl phthalate paste 18.0

(60/40 ratio) Methyl isobutyl ketone 20.0 Cellosolve acetate 20.0 Methylethyl ketone 50.0 Pigment TiO 5.0

After the ink containing the catalyst was applied to the surface of thefoamable top sheet, the sheet was dried without causing foaming by theapplication of gentle heat. A clear plastisol coating of Example 1 wasthen applied over' the printed, foamable, monomercontaining sheet andthe entire structure was then heated in an oven for 3 /2 minutes at atemperature of 385F.

Expansion of the foamable top sheet occurred to a significantly greaterextent in the unprinted areas than beneath the printed area, producing adecorative embossed appearance on the final, dimensionally stablesheet.-

What is claimed is:

l. The method of forming a flexible, cellular, dimensionally stableplastic surface covering which comprises forming a first and a secondfoamable plastisol by blending 1. a vinyl resin,

2. a plasticizer for said vinyl resin,

3. a blowing agent which decomposes at a temperature in the range abovethe glass transition temperature of the plasticized vinyl resin andbelow the decomposition temperature of said resin,

forming said first foamable plastisol into a gelled sheet and applyingto the top surface thereof, a nonfoamable vinyl resin plastisol coatingcontaining a reactive monomer compatible with the vinyl resin thereinand containing at least two olefinically unsaturated sites, and alsocontaining a catalyst that will cause polymerization and cross linkingof said monomer in said temperature range, gelling said nonfoamableresinous coating, applying a coating of said second foamable plastisolonto said gelled, nonfoamable resinous coating, gelling said secondfoamable plastisol coating, applying a final, clear, nonfoamableresinous coating onto said gelled second foamable plastisol coating andsubjecting the composite structure to sufficient heat to fuse the vinylresins, polymerize and cross-link the monomer, and decompose the blowingagent to form a cellular structure.

2. The method according to claim 1 wherein said vinyl resin comprisespoly(vinyl chloride).

3. The method according to claim 2 wherein the amount of blowing agentin the first formed foamable plastisol is different from the amount ofblowing agent in the second formed foamable plastisol.

4. The method according to claim 1 wherein the blowing agent isazodicarbonamide.

5. The method according to claim 1 wherein the monomer in thenonfoamable plastisol is present in the amount of from about 5 topercent by weight based on the weight of the resin.

6. The method according to claim 1 wherein said monomer comprisestrimethylol propane trimethacrylate.

7. The method according to claim 1 wherein the catalyst in thenonfoamable plastisol is lauroyl peroxide.

2. The method according to claim 1 wherein said vinyl resin comprisespoly(vinyl chloride).
 2. a plasticizer for said vinyl resin,
 3. ablowing agent which decomposes at a temperature in the range above theglass transition temperature of the plasticized vinyl resin and belowthe decomposition temperature of said resin, forming said first foamableplastisol into a gelled sheet and applying to the top surface thereof, anonfoamable vinyl resin plastisol coating containing a reactive monomercompatible with the vinyl resin therein and containing at least twoolefinically unsaturated sites, and also containing a catalyst that willcause polymerization and cross linking of said monomer in saidtemperature range, gelling said nonfoamable resinous coating, applying acoating of said second foamable plastisol onto said gelled, nonfoamableresinous coating, gelling said second foamable plastisol coating,applying a final, clear, nonfoamable resinous coating onto said gelledsecond foamable plastisol coating and subjecting the composite structureto sufficient heat to fuse the vinyl resins, polymerize and cross-linkthe monomer, and decompose the blowing agent to form a cellularstructure.
 3. The method according to claim 2 wherein the amount ofblowing agent in the first formed foamable plastisol is different fromthe amount of blowing agent in the second formed foamable plastisol. 4.The method according to claim 1 wherein the blowing agent isazodicarbonamide.
 5. The method according to claim 1 wherein the monomerin the nonfoamable plastisol is present in the amount of from about 5 to75 percent by weight based on the weight of the resin.
 6. The methodaccording to claim 1 wherein said monomer comprises trimethylol propanetrimethacrylate.
 7. The method according to claim 1 wherein the catalystin the nonfoamable plastisol is lauroyl peroxide.